The present invention relates to finishing machines of a type having a cylindrical screen for removing solids from juice or the like, and more particularly to a method and apparatus for automatically regulating operation of the finishing machine. It is particularly contemplated that the method and apparatus of the invention be employed in connection with the finishing of initial juices obtained, for example, from fruits, particularly citrus fruits, and vegetables such as tomatoes. Such juices commonly contain solids and it is generally desirable to regulate the amount of solids in a juice product obtained by finishing of the initial juice.
In the production of juices from various fruits and vegetables, juice extraction machines are commonly employed to first obtain an initial or raw juice containing substantial amounts of various solids such as rag, pulp from juice sacs, pectinous material, seeds, etc. Typical examples of juice extraction machines for obtaining initial or raw juice from various fruits and vegetables are disclosed, for example, in U.S. Pat. Nos. 2,631,625 and 4,170,935. The construction and method of operation contemplated for these machines is not of particular concern in connection with the present invention. Rather, the above-noted patents are referred to herein only for the purpose of demonstrating an exemplary source for the initial or raw juice with which the method and apparatus of the present invention are contemplated for use.
In order to produce commercially desirable juice from such initial or raw juice, it is generally necessary or desirable to first remove a substantial portion of the solid components from the initial juice to provide a so-called finished juice.
A typical commercial machine for converting initial or raw juice to a finished juice, characterized as being a screw-type finisher, is disclosed, for example, in Holbrook U.S. Pat. No. 3,370,527. In a finisher of this type, the initial juice or slurry is introduced into the interior of a stationary cylindrical screen. The screen is in effect a thin-walled cylindrical member, preferably formed from stainless steel, with very samll, closely spaced extrusion openings or perforations formed about its circumference and along its length.
Rotary screws for finishing machines are designed to have a fairly close tolerance fit within the cylindrical screen. The screw is rotated to conduct the initial juice or slurry along the axial length of the screen, forcing a liquid juice portion through the screen while a substantial portion of solids from the initial juice is retained upon the screen and conducted to a point of discharge. The finishing machine of the above-noted patent is at least partially described in greater detail below only for the purpose of assuring a complete understanding of the present invention.
However, the present invention is not limited to a particular type of finisher or even to a particular screw-type finisher as described above. For example, screw-type finishers tend to be of two different types. In one type, the screen and the outside diameter of the rotating screw element are tapered with the small diameter being located at the discharge end. The rotary screw is tapered and the pitch of its flights varies so that the cross-sectional area between the flights decreases at the discharge end. In other screw-type finishers, the screen and the outside diameter of the screw are cylindrical and are of generally constant diameter. The rotary screw may be conical with the large diameter at the discharge end, or the rotary screw may be cylindrical.
In both of the above types of screw finishers, an airloaded pulp or solids outlet valve is provided at the discharge end of the screen. As the fluid or juice component from the initial juice or slurry passes through the screen, substantial solids build up on the screen in a so-called "pad" area near the discharge end or solids outlet of the machine. Pressure in the cylinder is regulated to vary or adjust axial force applied to the valve in order to establish, maintain or selectively vary back pressure applied to the slurry solids by interaction of the outlet valve and screen.
In any event, regardless of the particular type of finishing machine being used, solids from the initial juice tend to build up on the screen and to plug the screen openings, thus interferring with continued operation and/or varying output characteristics of the finished juice product.
Solids build-up within the finishing machine and characteristics of the finished juice product tend to vary substantially, primarily because of operating conditions and characteristics of initial juice supplied to the finishing machine. Keeping in mind such variable operating conditions and variations in initial juice quality, it is generally an ultimate goal in finishing operations to recover as much of the liquid juice portion from the initial juice while maintaining acceptable juice quality as determined, for example, by "in-plant" standards and also requirements of various government agencies.
Considering as an exemplary application a finishing operation for citrus fruits, variations in initial juice supplied to the finishing machine may exhibit substantial variations in characteristics such as those set forth below:
(1) Initially, different characteristics will result for different types of fruit which may be processed in the same finishing operation, for example, various citrus fruits such as grapefruit, navel oranges, mandarin organes, lemons, etc.
(2) Even for a single type of fruit, the maturity of the fruit may affect both physical and chemical compositions of the initial juice.
(3) The degree of juice extraction accomplished with a juice extractor such as those described above may vary characteristics of the initial juice, for example, because of the quantity of membranous material, seeds, juice sacs and other non-juice components which are to be at least partially removed from the liquid juice by the finisher.
(4) Climate or weather may have substantial effects on quality of the fruit and accordingly quality of the initial juice. In this regard, it is believed obvious that quality of the initial juice will be affected by conditions such as freezing, heat waves, drought, etc., during the growth and maturity of the fruit.
(5) Climate and weather may also have an effect during the finishing operation itself. For example, operation of the finishing machine may be affected by weather conditions during the finishing operations. Furthermore, characteristics of the initial juice such as its temperature upon being introduced into the finishing machine will also depend upon climate or weather during the finishing operations.
(6) In addition to extraction characteristics described above, the rate of extraction may cause variations in the amount and quality of initial juice flow to the finisher due, for example, to changes in fruit size distribution, juice content of the fruit, extractor feeding efficiency and possibly unique standards established by a human operator controlling the extractor and finishing machines.
In the past, periodic adjustments have been made in the finishing machine to compensate for conditions such as those listed above. Such adjustments include changing of the hole size of the screen, adjustment of rotating speed for the screw and discharge valve pressure. Typically, changes in screen hole size and screw speed are made only infrequently, for example, once or twice a season, because of the substantial down time involved. On the other hand, discharge valve pressure adjustments may be made more frequently, typically, at least on a weekly or monthly basis.
In adjusting discharge valve pressure for finishing machines, it has generally been prior art practice to monitor output characteristics of the juice at selected intervals and to make any adjustments in the discharge valve pressure as may be required by that analysis. Accordingly, substantial variations may occur in quality of the finished juice product, particularly because of the amount and type of solids remaining in the juice. These characteristics in the finished juice product can be directly attributed to operation of the finishing machine. For example, solids or non-juice components increase in concentration as they are retained by the cylindrical screen in the finishing machine and move axially toward the solids outlet or discharge valve. The non-juice components or "pomace" become compacted near the discharge end of the finishing machine in a zone upon the cylindrical screen commonly referred to as the "pad" area. The length of the pad area varies somewhat depending on design and operating speed of the screw element. The amount of compression which occurs within the solids or pomace in the pad area in turn determines the amount of juice left in the pomace and the degree of dryness in the pomace as it is discharged through the valve area of the finishing machine. The compression or compaction of the pomace continues and increases until the pneumatic force applied to the valve is balanced or overcome. Thus, compaction and discharge of pomace or solids from the finishing machine occurs at a rate generally proportional to the amount of pomace in the initial juice supplied to the finishing machine, at least for a constant outlet valve pressure setting.
Pomace or non-juice particles (pulp particles) are also forced outwardly through the screen due to these compaction forces and form a portion of the finished juice product from the finishing machine. A certain amount of these particles is desirable in order to provide "body" within the finished juice. However, excessive amounts are undesirable in that they tend to cause bitterness in the juice and result in undesirably high viscosity.
Accordingly, there has been found to remain a need for a method and apparatus for automatically and accurately regulating the amount of solids in finished juice in order to assure that the finished juice meets high quality standards.